Dispatch Queue的種類
Serial Dispatch Queue 等待現(xiàn)在執(zhí)行中處理結(jié)束 (按照追加的順序, 先進(jìn)先出執(zhí)行).
創(chuàng)建Serial Dispatch Queue
dispatch_queue_t queue1 = dispatch_queue_create("queue1", NULL);
- 追加多個(gè)處理
dispatch_async(queue1, ^{
NSLog(@"1");
});
dispatch_async(queue1, ^{
NSLog(@"2");
});
dispatch_async(queue1, ^{
NSLog(@"3");
});
dispatch_async(queue1, ^{
NSLog(@"4");
});
dispatch_async(queue1, ^{
NSLog(@"5");
});
dispatch_async(queue1, ^{
NSLog(@"6");
});
- 執(zhí)行后的結(jié)果
2016-07-30 21:08:18.689 GCD[4114:268510] 1
2016-07-30 21:08:18.689 GCD[4114:268510] 2
2016-07-30 21:08:18.689 GCD[4114:268510] 3
2016-07-30 21:08:18.690 GCD[4114:268510] 4
2016-07-30 21:08:18.690 GCD[4114:268510] 5
2016-07-30 21:08:18.690 GCD[4114:268510] 6
有打印的結(jié)果可知道, Serial Dispatch Queue每次只能執(zhí)行一個(gè)任務(wù).
- 當(dāng)創(chuàng)建多個(gè)Serial Dispatch Queue的時(shí)候也可以達(dá)成類似Concurrent Dispatch Queue的效果, 但是創(chuàng)建過多你線程的話會(huì)消耗大量的內(nèi)存呢和CPU資源. 下列代碼:
dispatch_queue_t queue1 = dispatch_queue_create("queue1", NULL); dispatch_queue_t queue2 = dispatch_queue_create("queue2", NULL); dispatch_queue_t queue3 = dispatch_queue_create("queue3", NULL); dispatch_queue_t queue4 = dispatch_queue_create("queue4", NULL);- 追加任務(wù)
dispatch_async(queue1, ^{ NSLog(@"1"); }); dispatch_async(queue2, ^{ NSLog(@"2"); }); dispatch_async(queue3, ^{ NSLog(@"3"); }); dispatch_async(queue4, ^{ NSLog(@"4"); });- 打印出來的結(jié)果應(yīng)該是無序的
2016-07-30 21:16:22.883 GCD[4165:273436] 2
2016-07-30 21:16:22.883 GCD[4165:273478] 4
2016-07-30 21:16:22.883 GCD[4165:273443] 1
2016-07-30 21:16:22.883 GCD[4165:273469] 3
- 一般的在更新相同數(shù)據(jù)資源導(dǎo)致數(shù)據(jù)競(jìng)爭(zhēng)的時(shí)候會(huì)用到Serial Dispatch Queue
- Concurrent DisPatch Queue 不等待現(xiàn)在執(zhí)行中結(jié)束 (并行執(zhí)行).
- 創(chuàng)建Concurrent Dispatch Queue
dispatch_queue_t concurrentQueue = dispatch_queue_create("concurrentQueue", DISPATCH_QUEUE_CONCURRENT); dispatch_async(concurrentQueue, ^{NSLog(@"1");}); dispatch_async(concurrentQueue, ^{NSLog(@"2");}); dispatch_async(concurrentQueue, ^{NSLog(@"3");}); dispatch_async(concurrentQueue, ^{NSLog(@"4");}); dispatch_async(concurrentQueue, ^{NSLog(@"5");});- 執(zhí)行結(jié)果
2016-07-30 21:25:19.923 GCD[4221:278303] 3 2016-07-30 21:25:19.923 GCD[4221:278155] 2 2016-07-30 21:25:19.923 GCD[4221:278162] 1 2016-07-30 21:25:19.923 GCD[4221:278311] 4 2016-07-30 21:25:19.923 GCD[4221:278312] 5
通過執(zhí)行的結(jié)果可看出Concurrent Dispatch Queue的執(zhí)行方式
#### Main Dispatch Queue / Global Dispatch Queue
- s
```
dispatch_queue_t highGlobalQueu = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0);
dispatch_async(highGlobalQueue, ^{NSLog(@"1");});
dispatch_async(highGlobalQueue, ^{NSLog(@"2");});
dispatch_async(highGlobalQueue, ^{NSLog(@"3");});
dispatch_async(highGlobalQueue, ^{NSLog(@"4");});
dispatch_async(highGlobalQueue, ^{NSLog(@"5");});
```
- 四個(gè)優(yōu)先級(jí)
define DISPATCH_QUEUE_PRIORITY_HIGH 2
define DISPATCH_QUEUE_PRIORITY_DEFAULT 0
define DISPATCH_QUEUE_PRIORITY_LOW (-2)
define DISPATCH_QUEUE_PRIORITY_BACKGROUND
####dispatch_set_target_queue
- 優(yōu)先級(jí)
// 第一個(gè)參數(shù)是要變更優(yōu)先級(jí)的Queue, 第二個(gè)是被指定用到其優(yōu)先級(jí)的參數(shù)
dispatch_queue_t highGlobalQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0);
dispatch_queue_t mySerialQueue = dispatch_queue_create("mySerialQueue", NULL);
dispatch_set_target_queue(mySerialQueue, highGlobalQueue);
這個(gè)方法可以變更Queue的優(yōu)先級(jí), 還可以作為Dispatch Queue的執(zhí)行階層. Main Dispatch Queue 和 Global Dispatch Queue不能作為第一個(gè)參數(shù). 如果在多個(gè)Serial Dispatch Queue中指定一個(gè)目標(biāo), 那么原先在執(zhí)行的多個(gè)Serial Dispatch Queue, 在目標(biāo)Serial Dispatch Queue上只能執(zhí)行一個(gè)處理. 下面用代碼實(shí)現(xiàn)一下:
dispatch_queue_t queue1 = dispatch_queue_create("queue1", NULL);
dispatch_queue_t queue2 = dispatch_queue_create("queue2", NULL);
dispatch_set_target_queue(queue1, queue2);
// 打印一下
dispatch_async(queue1, ^{
NSLog(@"1");
});
dispatch_async(queue2, ^{
NSLog(@"2");
});
打印結(jié)果
2016-07-30 22:32:26.134 GCD[4621:305219] 1
2016-07-30 22:32:26.135 GCD[4621:305219] 2
我們會(huì)發(fā)現(xiàn)結(jié)果是順序排下來的, 這就說明在運(yùn)行的過程中, Serial Dispatch Queue 只同時(shí)執(zhí)行了一個(gè)處理
